CONTAMINATION RELATED TO ANTHROPIC ACTIVITIES . CHARACTERIZATION AND REMEDIATION 4 Enrichment of trace elements in the clay size fraction 5 of mining soils

13 Abstract Reactive waste dumps with sulfide minerals pro14 mote acid mine drainage (AMD), which results in water and 15 soil contamination by metals and metalloids. In these systems, 16 contamination is regulated by many factors, such as mineral17 ogical composition of soil and the presence of sorption sites 18 on specific mineral phases. So, the present study dedicates 19 itself to understanding the distribution of trace elements in 20 different size fractions (<2-mm and <2-μm fractions) of min21 ing soils and to evaluate the relationship between chemical 22 and mineralogical composition. Cerdeirinha and Penedono, 23 located in Portugal, were the waste dumps under study. The 24 results revealed that the two waste dumps have high degree of 25 contamination by metals and arsenic and that these elements 26 are concentrated in the clay size fraction. Hence, the higher 27 degree of contamination by toxic elements, especially arsenic 28 in Penedono as well as the role of clay minerals, jarosite, and 29 goethite in retaining trace elements has management implica30 tions. Such information must be carefully thought in the reha31 bilitation projects to be planned for both waste dumps.